The present invention relates to a magneto-optical recording medium and a magneto-optical recording and reproducing device which use a magnetic super-resolution method.
In magneto-optical disk devices which use the magnetic super-resolution method, a magneto-optical disk is used which is provided with a recording layer and with a reproducing layer having in-plane magnetization. In this type of magneto-optical disk device, during reproducing, a light beam is projected onto the reproducing layer side of the magneto-optical disk. Then, part of the area of the reproducing layer within the light beam spot is heated to above a predetermined temperature, and the magnetization of this portion (referred to as an aperture) shifts from in-plane magnetization to a perpendicular magnetization conforming to that of the recording layer beneath the aperture, i.e., the magnetization of the recording layer is copied to the reproducing layer. In this way, with this type of magneto-optical disk device, by reproducing the magnetization of the aperture, recorded marks smaller in diameter than the light beam spot can be reproduced.
In magneto-optical disk devices using this magnetic super-resolution method, it is preferable if the power of the light beam during reproduction (the reproducing power) is continuously at an optimum level. However, there are cases in which the optimum level of the reproducing power fluctuates with changes in the ambient temperature at the time of reproducing. For this reason, even if the current for driving the structure which produces the light beam (the driving current) is held constant, there are cases in which the reproducing power deviates from the optimum level.
If reproducing power is much stronger than the optimum level, the aperture formed on the magneto-optical disk becomes too large. Consequently, output of reproducing signals from tracks adjacent to the track being reproduced (crosstalk) is increased, the proportion of noise signals included in the reproduced data increases, and reading errors are more likely to occur.
Again, if reproducing power is much weaker than the optimum level, the aperture becomes smaller than the recorded mark, and the reproducing signal output from the target track is reduced. Accordingly, reading errors are more likely to occur in this case as well.
In a recording and reproducing device disclosed in Japanese Unexamined Patent Publication No. 63817/1996 (Tokukaihei 8-63817, published on Mar. 8, 1996) (U.S. Pat. No. 5,617,400), in order to control reproducing power, long marks and short marks formed on a magneto-optical disk are reproduced. These long and short marks are two types of recorded marks for reproducing power control of different mark lengths. In this device, reproducing power is controlled so as to bring close to a predetermined value a ratio of the quantities of the reproducing signals from these recorded marks. By this means, in this device, reproducing power is maintained at an optimum value, and the likelihood of reading errors is reduced.
FIG. 12 schematically shows a construction of a reproducing power control section in the recording and reproducing device of the above publication. Further, FIG. 13 is a schematic diagram showing a construction of a magneto-optical disk 30 used for the recording and reproducing device.
Prior to the explanation on the construction of the recording and reproducing device described in the publication, the construction of the magneto-optical disk 30 is firstly discussed. A track 320 is concentrically formed in the magneto-optical disk 30. A plurality of sectors 300 are successively formed in the track 320. As shown in FIG. 13, an address area 301, a reproducing power control area 302, and a data recording area 303 are formed in each of the sectors 300. The address area 301 is provided for recording information about a position of the sector. The reproducing power control area 302 is provided for recording a pattern of repeated short marks and a pattern of repeated long marks as recording marks for controlling reproducing power. The data recording area 303 is provided for recording digital data.
Here, the long mark is a mark having a larger diameter than the aperture, and the short mark is a mark having a shorter diameter than the aperture.
Next, referring to FIG. 12, the following explanation describes a reproducing operation in the recording and reproducing device. Firstly, when a light beam emitted from a semiconductor laser 32 reaches the address area 301 of the sector 300 on the magneto-optical disk 30, a sector address is recognized. And then, the emitted light is projected onto the reproducing power control area 302. Next, the light is reflected from a pattern of repeated long marks and short marks that is recorded in the area 302, and the light is converted to a reproducing signal by a photo-diode 33. The reproducing signal is inputted to an amplitude ratio detecting circuit 34. And an amplitude ratio detected in the amplitude ratio detecting circuit 34 is compared with a standard amplitude ratio by a differential amplifier 35, feedback is performed in a direction reducing a difference of the ratios, and a laser power control circuit 36 controls a driving current of the semiconductor laser 32.
After a driving current of a laser beam is controlled in such a manner so as to provide optimum reproducing power, the emitted light is projected to the area 303, the reproducing signal which has been read is inputted to a reproducing data processing circuit 37, and the likelihood of reading errors is reduced.
And then, when the emitted light reaches the next sector, the same operation is repeated so as to reset the optimum reproducing power.
In this way, the recording area of recording marks for controlling reproducing power is provided for each sector, and the quantity of reproducing signals for controlling reproducing power is detected for each sector, so that the reproducing power control can provide a response with a short time interval and correspond to short-time fluctuation of the optimum reproducing power.
However, the above magneto-optical reproducing method using the magnetic super-resolution method is more likely to be affected by a magnetic field from the outside because a signal is read based on a magnetic field stored in the recording medium and a temperature increase caused by radiation of a light beam. Namely, even when a length of the recording mark and the reproducing power remain the same, an amplitude of a signal may be changed according to the intensity of the external magnetic field.
The intensity of the external magnetic field varies due to leak of a magnetic field and others from an actuator of an optical head, and the intensity is also affected by a magnetic field from a recording mark recorded around a recording mark to be reproduced.
The intensity of the magnetic field from the surrounding recording mark depends upon a relationship between the recording mark to be reproduced and the surrounding recording mark with respect to size and polarity. Therefore, in the magneto-optical reproduction using the magnetic super-resolution method, an amplitude value of a reproducing signal may be varied depending upon a kind of recording mark recorded in adjacent tracks.
FIG. 14 is a graph showing measurement results of amplitude values regarding long and short marks (2T pattern and 8T pattern) relative to a change in reproducing power with respect to the following cases: when no recording mark is recorded in adjacent tracks of a track to be reproduced, and when a recording mark is recorded in the adjacent tracks with the same length as a recording mark belonging to a track to be reproduced. Here, a horizontal axis represents a reproduction power and a vertical axis represents an amplitude value (PEAK TO PEAK value).
According to the results, it is understood that when short marks are adjacent to each other, an amplitude value is hardly affected by the presence or absence of recording marks in adjacent tracks, and when long marks are adjacent to each other, an amplitude value sharply declines.
Further, FIG. 15 is a graph showing amplitude ratios of long and short marks (2T amplitude value/8T amplitude value) relative to a change in reproducing power regarding the following cases: when short marks are adjacent to each other, and when long marks are adjacent to each other. These ratios are obtained based on the measurement results of FIG. 14. A horizontal axis represents reproducing power and a vertical axis represents an amplitude ratio.
According to these results, when long marks are adjacent to each other, an amplitude ratio is considerably varied as compared to the case when no recording mark is recorded in the adjacent tracks of a track to be reproduced. This is because long marks being adjacent to each other result in a change in an external magnetic field of a reproducing layer in the magneto-optical disk, thereby changing an aperture diameter.
Therefore, regarding the same standard amplitude ratio, as compared with the case when no recording mark is recorded in tracks being adjacent to a track to be reproduced, when performing control in a state in which recording marks are recorded in the adjacent tracks, the control is exercised by larger reproducing power. As shown in the graph of FIG. 15, when no recording mark is recorded in the adjacent tracks at the target amplitude ratio of 0.5, the reproducing power is 2.4 mW, and when recording marks are recorded in the adjacent tracks, the reproducing power is 2.5 mW.
Namely, when an amplitude ratio is set such that a reproducing signal has an optimum signal quality, with reference to a state in which no recording mark is recorded in tracks being adjacent to a track to be reproduced, even if an amplitude ratio is set at the standard amplitude ratio, that is determined according to the above reference, reproducing power may be shifted from optimum reproducing power.
An objective of the present invention is to provide a magnetic super-resolution method magneto-optical recording medium and magneto-optical recording and reproducing device, that can reproduce a data recording area with high accuracy and optimum reproducing power without being affected by adjacent tracks.
In order to achieve the above objective, the magnetic super-resolution magneto-optical recording medium including a recording layer and a reproducing layer, is characterized in that recording marks for controlling reproducing power of a light beam are recorded at different positions between adjacent tracks in a radius direction, the recording mark being longer than a diameter of an aperture, which is formed on the reproducing layer by projecting thereon the light beam.
Like the conventional art, when long marks for controlling reproducing power of a light beam are adjacent to each other (formed at the same position between the adjacent tracks in a radius direction), an external magnetic field is varied on the reproducing layer of the magneto-optical disk during reproduction of information, so that an aperture diameter is likely to change. Therefore, when an amplitude ratio is determined so as to obtain an optimum reproducing signal with reference to a state in which no recording mark is recorded in tracks adjacent to the track being reproduced, in a state in which a recording mark is recorded in the adjacent tracks, even if an amplitude ratio is set at the standard amplitude ratio determined in accordance with the above reference, reproducing power is shifted from the actual optimum reproducing power. Hence, as described above, the present invention has a construction in which long recording marks for controlling reproducing power are formed at different positions between the adjacent tracks in a radius direction, so that it is possible to continuously reproduce a data recording area with high accuracy and optimum reproducing power without being affected by the adjacent tracks.
With the above arrangement, in the magneto-optical recording medium of the present invention, a resync pattern is preferably formed in a data recording area of a sector constituting the magneto-optical recording medium, and the recording mark is preferably recorded in the resync pattern.
Moreover, it is desirable that only a pattern for setting reproducing phase, that adjusts a phase of a reproducing clock, and short recording marks for controlling reproducing power, each of the short recording marks being smaller in diameter than the aperture, be recorded in a header area of the sector.
This arrangement makes it possible to reduce the header area of the sector and to achieve more efficient use of the magneto-optical recording medium.
Further, in order to achieve the aforementioned objective, the magneto-optical recording and reproducing device of the present invention, which carries out recording and reproducing for a magnetic super-resolution magneto-optical recording medium including the recording layer and the reproducing layer, is characterized by including a recording means which records long recording marks for controlling reproducing power of a light beam at different positions between adjacent tracks in a radius direction, each of the long recording marks being larger in diameter than an aperture formed on the reproducing layer by projecting thereon a light beam.
According to this arrangement, long recording marks for controlling reproducing power are recorded at different positions between adjacent tracks in a radius direction. Thus, it is possible to continuously reproduce the data recording area with high accuracy and optimum reproducing power without being affected by the adjacent tracks.
With this arrangement, in the magneto-optical recording and reproducing device of the present invention, it is desirable that the recording means further include a pattern generating means for generating different recording mark patterns (header pattern and resync pattern) between adjacent tracks.
The specific area is, for example, a resync pattern of a header area or a data recording area in a sector, which constitutes the magneto-optical recording medium.
The present invention is applicable to the construction for recording both a land track and a groove track of the magneto-optical recording medium. In such a construction, it is preferable to include a means for generating a recording mark pattern for a land track and a recording mark pattern for a groove track, wherein a record mark pattern corresponding to a track is recorded in each specific area such that the specific areas of the magneto-optical recording medium are aligned between the adjacent tracks in a radius direction.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.